Andy love the look of the white boards , these are self etch ? wow
the whole thing looks absolutely great .

Quote:

I may put a PDF together with complete details and PCB foils for all the "carrier" boards and 40 series modules (along with corrections to the ARP service manual - quite a few mistakes there!)

that really would be fantastic and very generous of you looking forward to it._________________In an infinite universe one might very well
ask where the hell am I
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I soldered lots way back in high school and I'm pretty sure I'll get any logic down pat, but it's the electronics formulas and testing I imagine will give me trouble.

Any plans for another fantastic retro build?

Truthfully? I think it may be ambitious for a first project... but Zthee's TTSH comes on a complete single board (except for the 3 VCO modules), so it's certainly easier to do than messing around with separate boards (23 PCB's in mine!).

I'm taking a break form building for a while, but I'm currently drawing up an Odyssey clone, which, I'm glad to say is a whole lot simpler

IMG_2720.JPG

Description:

Top row almost complete (Gate push switch needed)... Noise, Processors, S&H and Switch still to do. Not yet routed internally, but all working

I've increased the input resistors from the standard 100k to 330k (to compensate for the fact that I've swapped the 4012 for a 4075)... just wondering if I should take them up to 680k or more as on the Odyssey (0-5v waveforms, but 0-10 or +/-5 for the 2600) or ditch the passive mixing and put an op-amp in there... no cigar yet.

I've increased the input resistors from the standard 100k to 330k (to compensate for the fact that I've swapped the 4012 for a 4075)... just wondering if I should take them up to 680k or more as on the Odyssey (0-5v waveforms, but 0-10 or +/-5 for the 2600) or ditch the passive mixing and put an op-amp in there... no cigar yet.

GRRRRRR!!!!!

if i understand correctly you dont want to raise the input resistor cause of the low V, is it right?
if so why dont you boost the signal with this...(from your ody VCO post and working great!!!)

AndyR1960 wrote:

ericcoleridge wrote:

How do we increase the signal of the Oddy VCO? Is there a resistor that can be replaced or something?

Hi Eric,

I think this is what you want. I've lifted this from Thomas Henry's Build a Better Music Synthesizer - it's from his CEM VCO design. He used it on the Triangle output (which is also 0-5v PP) to convert it to 10v PP centered around zero.

I haven't tested it, but in theory it should be fine.

BTW, I've just taken a look at the 4023 VCF PCB foil I posted... definitely the same version as I've used to build my own VCF's. I wish I could be more help - could you PM some high rez images of your board to me, I'll see what I can do.

Andy.

and another thing...

AndyR1960 wrote:

LetterBeacon wrote:

would it just be a case of changing the value of the 100K feedback resistor?

Yes, I'd change the 100k resistor for a 51k and then follow it with a 50k trimmer to allow the voltage to be adjusted back down to 10v PP.

You may find that it's not *exactly* centered around zero, though it'll probably be fine for general use - otherwise I *think* you would need to change the value of the 300k resistor slightly.

i know its not like the original and i'm definitely not a pro but hey ...just trying to help

The only real problem I had was with the VCF - I didn't like the 4012 (Sorry to say this, but I'm a bit fed up with the Moog VCF hype, it's everywhere now) and replaced it with an Odyssey 4075 (which I had to botch to get to work)... I still wasn't 100% happy with the result, So I ended up searching for details on the 2600's 4072 VCF - not a lot of info available!

I ended up copying the tracks from a pretty bad photo of the back of a genuine 4072 module, then painstakingly sorting out where the components should go from the schematic that's available.

I was disappointed when it didn't work, but eventually (after 3 days) found that a 2N5459 had found it's way into my bag of 2N3906's causing the exponential pair to be duff.

Truthfully? I think it may be ambitious for a first project... but Zthee's TTSH comes on a complete single board (except for the 3 VCO modules), so it's certainly easier to do than messing around with separate boards (23 PCB's in mine!).

I actually think your way of doing individual boards is better. With one board it could get screwed up bad enough to have to scrap the whole thing. With individual boards only the module that is hosed can be replaced. There are going to be a few hobbyists whose skills won't be up to what's required for this project and will probably trash their board.

I just checked out your pictures on Flickr and you do fantastic work! My DIY ARP-2600 works very well but but can't touch the panels and cases you have made...excellent!

I just made four 4035 filters for a current project from your layout and they work great.

Thanks for posting your DIY projects!

Regards,

Theff

Thanks for your kind words Theff, much appreciated.

I set out 5 years ago with the though of building one, but didn't have any clue where to start - That's when I started dabbling with Odyssey VCO's etc and realised that it was a possibility.

Most of the stuff I've done is pretty crudely put together, but I went all out for the 2600 project as I wanted it to look as good as I could get it - I was initially put off by the price of having the panel laser cut and the screen printing, but I'm really pleased with the result - I seem to spend more time looking at it than playing with it

I'm currently working on the 3620 duophonic keyboard clone (the controller I've built is "ok", but just not quite right). Unfortunately, I had to pay a fair amount for decent and clear documentation as the available schematic downloads for the 3620 are unreadable... It should be completed by the end of the week, but I'm a bit concerned about what capacitors to use for the keyboard S&H. Standard metalized poly caps work well in the 4015 S&H module, but I'll have to see if they're good enough for the keyboard.

Andy I would recomend using polystyrene for sample and hold circuits
Rushonline capacitors are a good source for these and close to you._________________In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any

Andy I would recomend using polystyrene for sample and hold circuits
Rushonline capacitors are a good source for these and close to you.

Thanks for the info, they've got 500n in stock

I'm currently using a good quality metalized poly, which seems to work ok, I've just got to sort out a slight problem I have with the upper voice generation circuit (not scaling to 1v/oct)... I thought I'd just need to change a few resistor values to bring it in line, but it's having a knock-on effect to the main lower voice cv out.

holly crap Andy 500nf thats going to be physically quite large in a polystyrene cap. I have some 330nf polystyrenes - they are about the size of a sub c battery so yeah they are going to be big
last ones i used in a sample and hold were 10nf
(the MFOS 1v/oct keyboard circuit and rays sample and hold also)_________________In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any

Yup, they're big... The original 3620 Keyboard used BIG Polycarbonates, the polyester ones I'm using are fine for testing, but the voltage drop over time is not really acceptable.

But, at least I found the problem I had with the second voice CV scaling... It's the keyboard I used (converted from a matrix scanner - the carbon switch pads introduce too much additional resistance when a second note is played, causing havoc with the resistor chain).

I tested the PCB with the keybed from my Odyssey and it works fine... Looks like I'm going to have to build my own with J-Wires etc or get two MIDI CV converters - one low note and one high note priority... I can't see either being easy.

However maybe 2 resistor chains running opposite directions to each other could be utilised if you could come up with a way of preventing the second note on each being involved for each one , thinking lots of magnetic micro reed switches so probably painful to implement and to set up.

edit : oh or 2 of these one set to low note priority and one set to high note priority and a standard midi keyboard of course
http://www.kentonuk.com/products/items/m-cv/prosolo.shtml_________________In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any

Just bought some silver conductive paint - apparently less than 0.2r per cm, so I'll give that a try on the PCB pads and bubble contacts.

The ARP 3620 keyboard is duophonic from a single resistor chain - It derives the upper voice by detecting the voltage difference between the two notes played... that voltage difference is passed though a standard S&H and then mixed with the lower CV to produce the second upper voice - quite a simple but elegant design.

Kimber Allen, here in the UK, is going strong and still sell 2 pole "make" contact block assemblies - I'm waiting for them to get back to me, but I suspect they'll be expensive, but probably still cheaper than two Kenton Solo's

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